1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and in particular, to processing of an image such as a document image in which a feature image such as a tint block is embedded.
2. Description of the Related Art
There is a technique of embedding a feature image in an image to be transmitted in order to avoid tampering with a document or such. The feature image is, for example, a tint block. In the above-mentioned technique, for example, an image to be transmitted (for example, a document image) is converted into a tint block, the obtained tint block is embedded in the document image, and the document image in which the tint block is thus embedded is transmitted. Then, an apparatus which has received the transmitted document prints the received document image. After that, it is possible to determine whether the printed document image has been tampered with.
That is, the printed document image in which the tint block is embedded is scanned by means of a scanner. At this time, the tint block embedded in the document image is taken out directly from the scanned document image. Also, the scanned document image is again converted into tint block. Then, the tint block directly taken out from the document image is compared with the tint block converted from the document image. Then, in a case where the printed document image has been tampered with, the document image scanned by means of the scanner (after having been tampered with) is different from the document image before having been transmitted (before having been tampered with), because of the tampering. As a result, the tint block converted from the document image scanned by means of the scanner (after having been tampered with) is different from the tint block having been converted from the document image before having been transmitted (before having been tampered with) and having been embedded in the document image. In contrast thereto, the tint block directly taken out from the document image scanned by means of the scanner is the same as the tint block having been converted from the document image before having been transmitted (before having been tampered with) and having been embedded in the document image, as long as the tint block itself, having been embedded in the document image, has not been tampered with. Therefore, in the case where the document image has been tampered with, the tint block directly taken out from the scanned document image does not agree with the tint block converted from the scanned document image. Thus, it is possible to determine whether the document image has been tampered with by determining whether the tint block directly taken out from the scanned document image agrees with the tint block converted from the scanned document image.
For example, Patent Document 1 (i.e., Japanese Laid-Open Patent Application No. 2009-152651) discloses a technique of transmitting an image in which a tint block is embedded. In the technique, in a case where a printer to which the image is transmitted does not have a tint block processing function, a document processing apparatus from which the image is transmitted creates a document in which a tint block is combined (i.e., embedded) into a document image, and transmits the created document to the printer. On the other hand, in a case where the printer has the tint block processing function, the document processing apparatus does not combine the tint block into the document image, and transmits the document, as it is, to the printer. Thereby, since the document processing apparatus does not carry out combining the tint block into the document image in the case where the printer has the tint block processing function, it is possible to reduce a period of time of the processing carried out by the document processing apparatus.
Further, Patent Document 2 (i.e., Japanese Laid-Open Patent Application No. 2006-14189) discloses a printed matter processing system that carries out a check as to whether a document image has been tampered with. In this system, feature data is extracted from a content image obtained as a result of printed matter being scanned by a printed matter issuance apparatus. Then, a feature image such as a bar code is generated from the extracted feature data, the content image on which the feature image is superposed is printed, and thus, printed matter with the feature image is obtained. Then, a printed matter check apparatus extracts the feature image from a content image with the feature image, obtained from scanning the printed matter with the feature image, and restores the feature data from the extracted feature image. Further, the printed matter check apparatus extracts, from the content image with the feature image, the content image from which the feature image is removed, and extracts the feature data from the thus-extracted content image. Then, a check as to whether the content image has been tampered with is carried out by comparing the feature data restored from the feature image and the feature data extracted from the content image.